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  Surveying Instrument Collection 


Cooke, Troughton & Simms Ltd, York, U.K.


Automatic Level

Serial Number



270 x 130 x 135 mm



The three black-and-white figures are from Hogg, F.B.R., Armstrong, J.A. 1959. Two new Self-Aligning Levels, Empire Survey Review, Vol. 15, No. 111, pp. 2-6


This automatic level features a spot bubble (8'/2 mm), an extendable sun shade, a horizontal slow motions screw and clamp. Three foot screws are used for levelling and a 5/8 inch Withworth thread for centring. The crosshairs feature a horizontal wedge for measuring to line scale invar staffs.

The compensator and optical system of this instrument was developed conjointly by Hilger & Watts and Cooke, Troughton and Simms. The exteriors of the instruments differ slightly between the two brands.

The instrument in the collection does not feature the optional horizontal circle and the plane parallel plate micrometer.

Hogg & Armstrong (1959) explain the compensator shown in their Fig 6b as follows: "The swinging prism mount (1) is suspended by four steel alloy strips which are arranged in crossed pairs (2) on each side of it. The upper ends of the tapes are secured to blocks (3) keyed into a common bridge piece (4), which also carries the roof prism (5). Side flanges from the bridge piece provide the seating faces for the whole unit whilst walls (6) which project downwards outside the prism mount serve to secure the damper."

"The damper is necessary because the prism mount would oscillate indefinitely in its absence. The air-damper is formed by a cylindrical damping chamber in the swinging prism mount. In this chamber is mounted a damping piston (7) formed by two discs clamped one on each side of a plate (8). The radial clearance between the piston and the cylinder wall is very small. The end plates (9) limit the allowable swing of the prism mount and support it when the instrument is being carried."

The complete optical path though a slightly dislevelled (angle alpha) instrument is shown in another figure (Hogg & Armstrong 1959, Fig. 4). The roof prism (B) is fixed to the body of the telescope and the two other prisms (A, A') are suspended. F = plane of reticule, C = centre of crosshairs, OA = optical axis. The direction of HH' (horizontal line of sight) is deflected by an angle of 4 alpha from its original path and redirected to the centre (C) of the reticle.

According to Hogg & Armstrong (1959), an average accuracy of ±0.004 ft/mile (±0.8 mm/km) can be achieved with invar staffs and double run levelling with this automatic level.

History & comments

Cooke, Troughton & Simms Ltd was formed in York in 1922 from a merger of T. Cooke & Sons with Troughton & Simms. In 1924, the firm became a wholly owned subsidiary of Vickers and in 1963 part of Vickers Instruments. The company ceased trading in 1988.

Further information may be found in Hogg, F.B.R., Armstrong, J.A. 1959. Two new Self-Aligning Levels, Empire Survey Review, Vol. 15, No. 111, pp. 2-6 (+2 Plates)


in metal carrying case (340 x 196 x 200 mm), 2 of 4 clamps missing on box.


Some paint damage


Plaque in box lists: Cooke, Troughton & Simms Ltd as well as Agent: Precision Instrument Co., Sydney NSW.

The instrument was donated by Bill Rein, Balgowlah NSW, in April 2012


Catalogued on25 May 2015 by JMR. Colour photo by JMR.

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